A Problem of Change

One day, Isha’s mother gave her a 100-rupee note and asked her to buy a kilo of onion and half a kilo of potato from the market. After a while, Isha came back home and handed over the bag of vegetables to her mother and said, “The potatoes cost Rs.10 and the onions were Rs.20 a kilo. So, I paid the shopkeeper Rs.30″

“That’s good, Isha. Can I please have the balance money?” asked her mother.

Isha handed over the change to her mother.

On counting it, her mother realised that it was short by Rs.10.

“Did you spend money on anything else?” asked her mother.

“No, Mummy. This is the change given to me by the vegetable vendor,” said Isha.

“In that case, I think the vegetable vendor has either made a mistake or cheated you. He has given you Rs. 10 less. Did you count the change after he gave it to you?”

“I did,” said Isha.

“Then I think you have not calculated correctly,” said her mother.

On hearing this, Isha became sad.

“Don’t feel bad, Isha. You can improve your arithmetic skills with daily practice. Learning to calculate correctly will help you not just to score marks in your exams, but will be useful in your daily life too,” said her mother.

“I do try to practise, Mummy, but I find it difficult sometimes. Is there an easier way to learn to calculate?” asked Isha.


“Yes, there is. Let me teach you how to calculate using your fingers. Now, try to answer this by counting with your fingers: I have 10 mangoes and you have given me another 20 mangoes. How many mangoes do I have in all?”

Isha counted her fingers one by one. “One, two, three… 10. How do I count further?” she asked.

“Continue counting your fingers again from 11,” said her mother.

“Oh! Okay. So, 11, 12, 13…30!” she said finally. “30 mangoes!”

“Good, Isha. Now, let’s try subtraction. If I have 10 mangoes and I give away 3 to our neighbours, how many mangoes will remain with me?” asked her mother.

Isha held up 10 fingers and folded 3. “Seven!” she replied triumphantly.

“Very good! Now, I’ll teach you how to subtract larger numbers like 100 minus 30,” said her mother and began doing the sum on paper. Isha observed her attentively and then answered, “70!”

“That’s right. See, how easy learning to calculate can be. With daily practice, you will be able to add and subtract faster. Now, let’s go to the market and ask the vegetable vendor for the balance,” said Isha’s mother.


“And perhaps he is weak in calculating too. I will teach him a few calculations,” said Isha.

“Ha ha! You are already a master mathematician!” laughed her mother.